Steel tube rolling mill high-chromium guide disc, casting mold system and preparation method

Abstract

The invention provides a high-chromium guide disc of a steel tube rolling mill, a casting mold system and a preparation method. The high-chromium guide disc is prepared by adopting a multi-element composite reinforcing material and a new casting mold system and adopting a reasonable preparation process and a heat treatment method; a vertical pouring gate is arranged on a casting system of the guide disc and connected with molten steel pouring gates and dead heads of a plurality of uniformly distributed horizontal pouring gates, and a system platform supported by a platform bracket is arranged below the casting system; in the preparation process, graphite particles are added into molding sand to improve the uniform cooling capacity of a sand box; graphite is promoted to be converted from a flake shape to a spherical shape through a spheroidizing process, a fine and uniformly-distributed high-chromium casting is obtained, and the plasticity and toughness of the casting are improved; the comprehensive performance such as strength, hardness and wear resistance of the guide disc is greatly enhanced, the problem that steel bonding is prone to occurring in the rolling process of an existing alloy nodular cast iron guide disc is solved, the use performance of the guide disc is greatly improved, the service life of the guide disc is greatly prolonged, meanwhile, materials of products are saved, and manufacturing and production cost is reduced.

Description

Technical Field

[0001] The invention relates to a manufacturing technology for steel tube rolling mill parts, in particular to a high-chromium guide plate for a puncher or a precision tube rolling mill in the production of hot-rolled seamless steel tubes, a casting system and a preparation method. Background Art

[0002] The commonly used two-roller steel pipe piercing machine uses two guide plates arranged up and down and two horizontally arranged rollers to form a transverse closed hole. When the tube billet at 1200℃~1270℃ passes through the transverse closed hole, the steel pipe head passes through the tube billet to complete the piercing process of the hot-rolled seamless steel pipe. During work, the guide plate actively gives the tube billet an additional axial forward force, increases the piercing speed of the steel pipe, and reduces the axial backward sliding and inward folding of the tube billet. The precision tube rolling mill also uses two guide plates arranged up and down and two horizontally arranged rollers to form a transverse closed hole. The 1100℃ tube billet passes through it to complete the deformation of the seamless steel pipe in the production process. The guide plate of the steel tube rolling mill is subjected to high stress wear due to rolling and sliding friction of compressive stress at high temperature, and is also subjected to the chilling, heating and corrosion of cooling water. The working environment is harsh and the consumption is large.

[0003] The existing steel pipe guide plate is a large ductile iron casting with a diameter of 1500-2900mm and a single piece weight of 1.5-5.5 tons / piece. It is very difficult to spheroidize. Its strength and hardness are both low. The general tensile strength σb is about 400MPa, and the surface macroscopic hardness is about HRC30, which leads to poor overall performance of the guide plate. At present, the material of the steel pipe guide plate is alloy ductile iron, and its main components are: carbon C: 3.0-3.5; silicon Si: 1.4-2.2; manganese: Mn0.3-0.8; nickel Ni: 1.5-2.0; chromium Cr: 0.3-0.8; molybdenum Mo: 0.1-0.2; phosphorus P: ≤0.1; sulfur S: ≤0.015; used in normalized state. The nickel Ni content in the material is also high, which greatly increases the material cost.

[0004] Due to the poor strength, hardness and wear resistance of the steel pipe guide disc, it is very easy to produce "steel sticking" phenomenon during the rolling process, causing surface damage to the rolled steel pipe. Ductile iron is susceptible to corrosion when water-cooled in a high-temperature working environment, and it is easy to form a patch of pitting on the surface, which also affects the surface quality of the steel pipe. Therefore, the guide disc needs to be replaced frequently during work, and the frequent replacement not only increases the production cost, but also seriously affects the normal production. Summary of the invention

[0005] In order to solve the problems of short service life, easy "sticking to steel", and poor corrosion resistance caused by low hardness and strength of the guide disc for hot-rolled seamless steel pipes during use, the present invention proposes a new high-chromium material guide disc for steel pipe rolling mills and a new casting system designed for the guide disc, and prepares the high-chromium guide disc for steel pipe rolling mills through a reasonable preparation method. The present invention includes the following three technical solutions:

[0006] A technical solution of the present invention is to propose a high chromium guide disc for a steel tube rolling mill, characterized in that its composition is calculated by weight as follows: C: 1.5% to 1.7%, Si: 0.6% to 1.0%, Mn: 0.4% to 0.8%, P: ≤0.04%, S: ≤0.02%, Cr: 12.0% to 13.0%, Al: 3.6% to 4.0%, Ni: 0.2% to 0.3%, Mo: 0.1% to 0.2%, Nb: 0.1% to 0.2%, Y: 0.02% to 0.025%, Ce: 0.09% to 0.11%, N: 0.008% to 0.01%, and the remainder is Fe and other inevitable impurities. The composition of the components is preferably calculated by weight as follows: C: 1.6%, Si: 0.8%, Mn: 0.6%, P: ≤0.04%, S: ≤0.02%, Cr: 12.5%, Al: 3.8%, Ni: 0.25%, Mo: 0.15%, Nb: 0.15%, Y: 0.02%, Ce: 0.10%, N: 0.009%, and the remainder is Fe and other inevitable impurities.

[0007] Another technical solution of the present invention is to propose a high-chromium guide disk casting system for a steel pipe rolling mill, characterized in that a guide disk cavity is arranged above the casting system, and a system platform and a platform bracket are arranged below; a molten steel runner and a riser are arranged above the guide disk cavity, and the molten steel runner is arranged with a vertical runner in the middle connecting several evenly distributed horizontal runners, and several risers are evenly distributed between the horizontal runners; the molten steel runner and the riser are both connected to the guide disk cavity.

[0008] The technical solution is also characterized in that the outer circle and the lower part of the guide plate cavity adopt an improved sand mold, and the sand mold forming the guide plate cavity is placed in a ring-shaped sand box with an inner hole; from the upper part of the ring-shaped sand box to the center of the inner hole, the several horizontal runners of the molten steel runner are evenly distributed in the upper part of the guide plate cavity. The system platform is a circular platform with a diameter larger than the outer circle of the ring-shaped sand box, and the ring-shaped sand box is set on the system platform supported by the platform bracket. The riser is set above the guide plate cavity near the inner hole.

[0009] Another technical solution of the present invention is to provide a method for preparing a high chromium guide disc for a steel tube rolling mill, characterized in that the high chromium guide disc is prepared by using the component composition and casting system of the high chromium guide disc, and the method is as follows:

[0010] 1) preparing a circular sand box with an inner hole in the guide plate cavity; adding 60-75% of the total weight of graphite particles to the molding sand to prepare an improved sand mold, wherein the outer circumference and the lower part of the guide plate cavity 1 adopt the improved sand mold to increase the uniform cooling capacity of these parts;

[0011] 2) Molten steel is smelted according to the composition range of the guide plate, and the tapping temperature is 1460℃~1490℃; before tapping, 1kg of silicon-zirconium inoculant per ton of molten steel and Y and Ce elements that meet the composition content range are put into the ladle and then poured into the molten steel to spheroidize the alloy;

[0012] 3) After steel is tapped, argon is blown into the ladle for 30 seconds to calm it down to 1370℃~1400℃ for casting;

[0013] 4) Molten steel is poured through the vertical runner of the casting system and flows evenly to each horizontal runner until the molten steel in the circular ring sand box of the guide plate cavity fills the casting from bottom to top, thereby obtaining a guide plate blank; then the cast guide plate blank is subjected to conventional annealing and rough processing;

[0014] 5) After rough machining, the guide plate is subjected to salt bath isothermal quenching and tempering heat treatment process; the heating temperature of salt bath isothermal quenching is 920-950°C, the isothermal temperature is 290°C-320°C, and the isothermal time is 60-90min; the tempering temperature is 420°C, and the secondary tempering is 200°C;

[0015] 6) After the heat treatment is completed, the guide plate is machined into a finished product.

[0016] The technical solution is also characterized in that conventional steps such as argon blowing during the molten steel smelting process are carried out according to conventional methods to ensure the smelting quality of the molten steel.

[0017] The technical solution is further characterized in that the guide disc material composition range is preferably selected in the following proportions by weight: C: 1.6%, Si: 0.8%, Mn: 0.6%, P: ≤0.04%, S: ≤0.02%, Cr: 12.5%, Al: 3.8%, Ni: 0.25%, Mo: 0.15%, Nb: 0.15%, Y: 0.02%, Ce: 0.10%, N: 0.009%, and the balance is Fe and other inevitable impurities for molten steel smelting of the guide disc material. The guide disc has a tensile strength of 550MPa to 650MPa and a surface hardness of HRC40 to 55.

[0018] The present invention adds elements that improve heat resistance, high temperature oxidation resistance and toughness to the high chromium guide disc material of the steel tube rolling mill through improved design of the guide disc components and the use of a new casting system and preparation method, thereby greatly improving the high temperature wear resistance of the guide disc. The present invention adds a spheroidizing process to improve the toughness and high temperature resistance of the material. The inserted sand mold of the present invention ensures the casting quality of the working layer and promotes the solidification sequence from bottom to top, and the ventilation function of the lower part of the system platform further improves the good sequence of casting solidification. The heat treatment process of the present invention adopts a salt bath isothermal quenching process to further enhance the overall comprehensive performance of the product. The present invention can be used to replace the current alloy ductile iron guide disc to solve the problems of poor wear resistance, low life, easy to produce "steel sticking" phenomenon and serious impact on the normal production of seamless steel pipes. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the overall structure of the guide plate cavity, pouring and rigging system and platform of the present invention;

[0020] Figure 2 It is a schematic diagram of the cross-sectional structure of a casting sand mold;

[0021] Figure 3 It is a schematic diagram of the cross-sectional structure of the guide plate of a steel tube rolling mill.

[0022] The serial numbers are: guide plate cavity 1, molten steel runner 2, riser 3, conventional sand mold 4, improved sand mold 5, system platform 6, platform bracket 7. DETAILED DESCRIPTION

[0023] The following is the attached Figures 1 to 3 The following drawings show preferred embodiments, which do not limit other implementations of the present invention.

[0024] The purpose of the present invention is to solve the problems of low hardness, low strength and "steel sticking" in the use of guide discs for hot-rolled seamless steel pipes, and to propose a new type of high-chromium material guide disc, casting system and preparation method. Through the new design of the guide disc composition and the new casting process and heat treatment method, the comprehensive performance of the product is enhanced, and it is used to replace the current alloy ductile iron guide disc to solve the shortcomings of poor wear resistance, easy to produce "steel sticking", especially seriously affecting the production of thin-walled seamless steel pipes and alloy seamless steel pipes.

[0025] The high chromium guide disc of the present invention is applied to the punching machine or precision tube rolling machine of hot-rolled seamless steel pipes. The present invention adds a multi-component composite strengthening material to the material of the high chromium guide disc to improve heat resistance and high-temperature oxidation resistance as well as toughness, that is, the alloy element content should not be too high, which can reduce the material cost and improve its high-temperature wear resistance and corrosion resistance. The present invention adds a spheroidizing process, and uses the spheroidizing process to refine the material structure, reduce the generation of network carbides, and improve the toughness and temperature resistance of the material. Through the design of a strong heat-absorbing casting structure, its casting performance is improved, so that the guide disc has a sufficiently thick working layer to meet the needs of multiple repairs during use. The large-scale workpiece salt bath isothermal quenching heat treatment process is adopted to further improve the overall comprehensive performance of the steel tube rolling mill guide disc, thereby improving the product's performance and service life. Through the above-mentioned improved design, the tensile strength of the steel tube rolling mill guide disc reaches 490-550MPa, and the surface macroscopic hardness reaches HRC40-52, which meets the use requirements of the steel tube rolling mill guide disc.

[0026] The present invention designs a new type of high-chromium material according to the service conditions and technical requirements of the guide plate of the steel pipe rolling mill, which replaces the alloy ductile iron material used at home and abroad, so that the guide plate has higher comprehensive performance to meet the production needs of the steel pipe. The composition design of the guide plate of the present invention is calculated by weight, and its content is: C: 1.5% to 1.7%, Si: 0.6% to 1.0%, Mn: 0.4% to 0.8%, P: ≤0.04%, S: ≤0.02%, Cr: 12.0% to 13.0%, Al: 3.6% to 4.0%, Ni: 0.2% to 0.3%, Mo: 0.1% to 0.2%, Nb: 0.1% to 0.2%, Y: 0.02% to 0.025%, Ce: 0.09% to 0.11%, N: 0.008% to 0.01%, and the rest is Fe and other inevitable impurities.

[0027] In high-chromium materials, C and Cr are the most basic and important alloying elements. The amount of their content determines the number of carbides, hardness, toughness and hardenability of the material. Cr can increase the hardenability of steel and has a secondary hardening effect. It can improve the hardness and wear resistance of carbon steel without making the steel brittle. When the Cr content exceeds 12%, the steel has good high-temperature oxidation resistance and oxidation corrosion resistance and can increase the thermal strength of the steel. At the same time, considering the needs of the spheroidizing process, the present invention sets the C content to 1.5-1.7%, the Cr content to 12-13%, and the chromium-carbon ratio to 7.1-8.7%. When the chromium-carbon mass ratio is greater than 5, the carbides can be of moderate size and dispersed evenly, which is beneficial to improving the wear resistance of the alloy.

[0028] Element Si is an indispensable deoxidizing element and graphitizing element in the smelting process, but because it has the effect of reducing hardenability, the present invention sets the Si content to 0.6-1.0%. Element Mn both enters carbides and dissolves in the matrix, and the present invention sets the Mn content to 0.4-0.8%.

[0029] Element P is an inevitable harmful trace element in the raw material, which is harmful to the high-temperature deformation performance of the material. During the heat treatment process, diffusion segregation to the grain boundaries leads to embrittlement. The present invention controls its content below 0.04%. Element S is a strong anti-graphitizing element, so the content should be as low as possible. The present invention controls its content below 0.02%. Element Al can take the lead in forming a continuous and dense protective film on the metal surface at high temperatures, effectively improving the high-temperature oxidation resistance. Al also has the functions of deoxidation and grain refinement. It is a strong graphitizing element. The present invention sets the Al content to 3.6-4.0%. Element Ni can be completely dissolved in the matrix, which plays a role in strengthening the matrix and improving the comprehensive performance of the material, and can also improve the hardenability. The present invention sets the Ni content to 0.2-0.3%

[0030] The present invention sets the Mo content to 0.1-0.2%. About 50% of the element Mo in the high-chromium material enters into Mo2C, and about 25% enters into M7C3 carbides, which can effectively improve the hardness and wear resistance; in addition, about 23% is dissolved into the matrix, which can significantly improve the hardenability of the material. The Nb element can refine the austenite grains, improve the strength and toughness of the material, and change the growth state of the eutectic structure. The present invention sets the Nb content to 0.1-0.2%. The element Y is set to 0.02-0.25%. The Y element has a strong spheroidizing effect, which can effectively improve the mechanical properties of cast iron, reduce the formation of network carbides, improve the high-temperature consistency of high-chromium materials, improve the casting performance of high-chromium materials, and reduce the generation of defects such as shrinkage.

[0031] The present invention also adds 0.09-0.11% of rare earth Ce, which has a strong spheroidizing effect, can significantly refine the microstructure of the steel, and has better high-temperature strength and toughness, thereby obtaining better hot ductility. Element N has a solid solution strengthening effect, which can improve the hardenability, strength and impact toughness of the steel, and the element N is set to 0.008%-0.01%. The Al, Ni and Nb elements in the composition of the present invention are all graphitizing elements, which can refine the grains of the material, improve the strength, toughness and hardenability, and improve the overall comprehensive performance of the material.

[0032] Reference Figure 1 The present invention has carefully designed a high-chromium guide plate casting system for a steel tube rolling mill. The casting structure of the system enables the present invention to obtain a relatively accurate guide plate blank. The overall structural form of the guide plate casting system is as follows: Figure 1As shown, the casting system is provided with a guide plate cavity 1 above, and a system platform 6 and a platform bracket 7 below; a molten steel runner 2 and a riser 3 are provided above the guide plate cavity 1, and the molten steel runner 2 is provided with a vertical runner in the middle connecting a number of evenly distributed horizontal runners, and a number of risers 3 are evenly distributed between the horizontal runners; the molten steel runner 2 and the riser 3 are both connected to the guide plate cavity 1.

[0033] The guide plate cavity 1 of the present invention is designed as a toroidal sand box with an inner hole, and the sand mold forming the guide plate cavity 1 is placed in the toroidal sand box with an inner hole. The outer circle and the lower part of the guide plate cavity 1 adopt an improved sand mold 5, and the remaining part adopts an ordinary sand mold 4. The use of the improved sand mold 5 strongly increases the uniform cooling capacity of the casting and improves the good solidification sequence from bottom to top in the casting. A vertical molten steel runner 2 is arranged from the top of the guide plate cavity 1 to the center of the inner hole, and the lower part of the molten steel runner 2 is connected to a plurality of horizontal runners evenly distributed above the guide plate cavity 1, and a plurality of casting risers 3 are evenly distributed between the horizontal runners near the inner hole of the upper end surface of the guide plate cavity 1.

[0034] The casting system of the present invention adopts a middle straight runner to connect several evenly distributed horizontal runners. The design concept is that the horizontal runner is the upper runner, and the molten steel poured in first is at the bottom, filling the casting mold from bottom to top, which is conducive to the molten steel quickly and evenly filling the casting mold and solidifying evenly in sequence. Multiple evenly distributed casting risers 3 are arranged on the upper end surface of the guide plate cavity 1 near the inner hole, so that possible casting defects are far away from the working surface of the guide plate, that is, the outer cylindrical surface of the guide plate, such as Figure 3 shown.

[0035] The system platform 6 of the guide plate of the present invention is a circular platform with a diameter larger than the outer circle of the annular flask, and the annular flask is arranged on the system platform 6 supported by the platform bracket 7. The lower part of the system platform 6 is supported by a plurality of platform brackets 7, forming a freely ventilated space, which is convenient for the rapid solidification of molten steel from bottom to top, and artificial exhaust can be performed when necessary.

[0036] The invention adopts the composition of high chromium guide disc of steel tube rolling mill and high chromium guide disc casting system, and adopts the high chromium guide disc preparation method of the invention to prepare the guide disc of steel tube rolling mill.

[0037] 1) A circular sand box of the guide plate cavity 1 is prepared by using a conventional sand mold 4 and an improved sand mold 5. In order to improve the uniform cooling capacity of the guide plate cavity 1 and form a good rapid solidification sequence, a special improved sand mold 5 is also designed in part of the guide plate cavity 1, that is, graphite particles of 60 to 75% of the total weight of the molding sand are added to the molding sand. The improved sand mold 5 is distributed in the lower part and the outer circumference of the guide plate cavity 1, such as Figure 2 shown.

[0038] 2) Molten steel is smelted according to the range of the guide plate composition content, and the tapping temperature is 1460℃~1490℃; before tapping, 1kg of silicon-zirconium inoculant per ton of molten steel and Y and Ce elements within the composition content range according to the present invention are placed in a ladle and then poured into the molten steel for alloy spheroidization. Alloy spheroidization effectively promotes the transformation of graphite from flake to spherical, inhibits the formation of network carbides, reduces defects such as shrinkage cavities and looseness, and improves the plasticity and toughness of the casting.

[0039] 3) After steel is tapped, argon is blown into the ladle for 30 seconds to calm it to 1370℃~1400℃ for casting. The conventional steps such as argon blowing in the steelmaking process are carried out in the conventional way to ensure the quality of the molten steel.

[0040] 4) Molten steel is poured through the vertical runner of the guide plate cavity 1 and flows evenly to each horizontal runner until the molten steel fills the mold from bottom to top, thereby obtaining a guide plate blank. Afterwards, the cast guide plate blank is subjected to conventional annealing and rough machining.

[0041] 5) After rough machining, the guide plate is subjected to salt bath isothermal quenching and tempering heat treatment process; the heating temperature of salt bath isothermal quenching is 920-950℃, the isothermal temperature is 290℃-320℃, and the isothermal time is 60-90min; the tempering temperature is 420℃, and the secondary tempering is 200℃. The salt bath isothermal quenching has an adjustable cooling rate, which has the characteristics of fast high temperature cooling rate and slow low temperature cooling rate, which is conducive to controlling the deformation of the casting and can meet the quenching requirements of castings with different wall thicknesses. Compared with oil and water quenching, salt bath quenching has smaller quenching stress and less tendency to thermal cracking. Therefore, the surface quality of the casting is higher.

[0042] 6) After the heat treatment is completed, the guide plate is machined into a finished product.

[0043] The preferred range of the composition of the guide plate of the present invention is calculated by weight as follows: C: 1.6%, Si: 0.8%, Mn: 0.6%, P: ≤0.04%, S: ≤0.02%, Cr: 12.5%, Al: 3.8%, Ni: 0.25%, Mo: 0.15%, Nb: 0.15%, Y: 0.02%, Ce: 0.10%, N: 0.009%, and the balance is Fe and other inevitable impurities. The tensile strength of the guide plate product is 550MPa-650MPa, and the surface hardness is HRC40-52.

[0044] The guide plate casting mold design and preparation method of the present invention achieves the purpose of rapid and uniform mold filling and rapid sequential solidification during casting, thereby ensuring the performance and quality of the guide plate casting.

[0045] Example 1

[0046] See attached Figure 1-3In this embodiment, a pair of high chromium guide discs for punching machines is manufactured, with a total of 2 pieces. The maximum outer diameter of the guide disc blank is Φ2850mm, the minimum outer diameter is Φ2750mm, the inner hole is Φ2130mm, the height is 385mm, and each piece weighs 6900kg.

[0047] The composition (weight %) of the punch guide plate is as follows:

[0048] C Si Mn P S Cr Al Ni Mo Nb Y Ce N 1.6 0.8 0.6 0.03 0.017 12.5 3.8 0.25 0.15 0.15 0.02 0.1 0.009

[0049] The rest is Fe and other inevitable impurities. The casting molds use conventional sand mold 4 and improved sand mold 5, and the graphite particle content in the improved sand mold 5 in the casting mold is 75%.

[0050] like Figure 1 As shown, the sprue of the molten steel runner 2 of the guide plate cavity 1 in this embodiment is connected to 6 evenly distributed horizontal runners, and 6 evenly distributed casting risers 3 are arranged between the 6 evenly distributed horizontal runners, and the position of the risers 3 is close to the inner hole of the guide plate cavity 1. In order to ensure the shrinkage compensation effect, this embodiment adopts heat preservation heating risers.

[0051] In this embodiment, during smelting, the addition of elements Y and Ce according to the content range of claim 1 and the silicon zirconium inoculant at a ratio of 1 kg per ton of molten steel are placed in the ladle before tapping and then poured into the molten steel; the tapping temperature is 1480°C, and after tapping, argon is blown in the ladle for 30 seconds and then calmed to 1380°C for casting. After obtaining the blank, conventional annealing and rough processing are carried out, and then quenching and tempering treatment is carried out. The quenching and tempering process is: heating temperature is 930°C, isothermal temperature is 310°C, and isothermal time is 80 minutes. The tempering temperature is 420°C, and secondary tempering is carried out at 200°C.

[0052] After quenching and tempering, this embodiment is subjected to conventional machining to the finished product. Six tests were evenly distributed at the minimum outer diameter of the working surface of the guide disc, and the hardness results were HRC values ​​of the first piece: 41.5, 42.3, 42.2, 41.9, 41.7, 42.1, and an average of 41.95 HRC; the conjoined specimens were tested for tensile properties, and the results were σb values ​​of 580 MPa, 610 MPa, 598 MPa, and an average of 596 MPa. The second piece HRC values: 42.5, 41.3, 41.6, 41.8, 42.4, 42.3, and an average of 41.98 HRC; the conjoined specimens were tested for tensile properties, and the results were σb values ​​of 587 MPa, 604 MPa, 608 MPa, and an average of 599 MPa.

[0053] After installation and use, the service life of this embodiment is increased by 4.5 times compared with the original ductile iron guide disc. When it is scrapped, the measured outer diameter of the working surface is reduced by 80 mm, and the surface hardness is still around 41HRC, which greatly reduces the material and production costs.

[0054] Example 2

[0055] This embodiment is to manufacture a pair of high chromium guide discs for precision tube rolling mill, a total of 2 pieces. The maximum outer diameter of the guide disc blank is Φ1984mm, the minimum outer diameter is Φ1912mm, the inner hole is Φ1335mm, the height is 185mm, and each piece weighs 1758kg.

[0056] The composition (weight %) of the guide plate of the tube rolling mill is as follows:

[0057] C Si Mn P S Cr Al Ni Mo Nb Y Ce N 1.68 0.9 0.87 0.03 0.02 13 3.9 0.3 0.19 0.2 0.024 0.11 0.01

[0058] The rest is Fe and other inevitable impurities. The content of graphite particles in the improved sand mold 5 in the casting mold is 62%.

[0059] like Figure 1 As shown, the sprue of the molten steel runner 2 of the guide plate cavity 1 of this embodiment is connected to four evenly distributed horizontal runners, and four evenly distributed casting risers 3 are arranged between the four evenly distributed horizontal runners, and the positions of the risers are close to the inner hole of the guide plate cavity 1. In order to ensure the shrinkage compensation effect, this embodiment adopts a heat-insulating riser.

[0060] During smelting, the present embodiment adds Y and Ce elements that meet the content range and a silicon-zirconium inoculant at a ratio of 1 kg per ton of molten steel. Before tapping, the molten steel is poured into the ladle after being put into the ladle. The tapping temperature is 1460°C. After tapping, argon is blown in the ladle for 30 seconds and then calmed to 1370°C for casting. After obtaining the blank, conventional annealing and rough machining are carried out, and then quenching and tempering treatment is carried out. The quenching and tempering process is as follows: the heating temperature is 920°C, the isothermal temperature is 300°C, and the isothermal time is 75 minutes. The tempering temperature is 420°C, and secondary tempering is carried out at 200°C.

[0061] After quenching and tempering, this embodiment is subjected to conventional machining to the finished product, and the hardness test is performed at the minimum outer diameter of the working surface. The hardness test results at 6 evenly distributed locations are HRC values: 51.5, 52.0, 50.9, 51.7, 50.8, 51.3, with an average of 51.4 HRC; the conjoined specimens are subjected to tensile performance testing, and the results are σb values ​​of 551 MPa, 550 MPa, 548 MPa, respectively, with an average of 550 MPa. The second piece HRC values: 51.6, 51.3, 51.4, 52O, 51.4, 51.7, with an average of 51.6 HRC; the conjoined specimens are subjected to tensile performance testing, and the results are σb values ​​of 541 MPa, 543 MPa, 540 MPa, respectively, with an average of 541 MPa.

[0062] After installation and use, the service life of this embodiment is increased by 5 times compared with the original ductile iron guide disc. When it is scrapped, the outer diameter of the working surface is reduced by 90mm, and the surface hardness is still around 50HRC, which greatly reduces the cost of use.

[0063] Example 3

[0064] This embodiment is a pair of high chromium guide discs for hot-rolled seamless steel pipes, a total of 2 pieces. The maximum outer diameter of the guide disc blank is Φ2550mm, the minimum outer diameter is Φ2450mm, the inner hole is Φ1930mm, and the height is 290mm.

[0065] The composition (weight %) of the guide plate is as follows:

[0066] C Si Mn P S Cr Al Ni Mo Nb Y Ce N 1.51 0.5 0.45 0.03 0.02 12 3.6 0.2 0.11 0.1 0.02 0.09 0.008

[0067] The rest is Fe and other inevitable impurities. The content of graphite particles in the improved sand mold 5 in the casting mold is 70%.

[0068] like Figure 1 As shown, the sprue of the molten steel runner 2 of the guide plate cavity 1 of this embodiment is connected to 6 evenly distributed horizontal runners, and 6 evenly distributed casting risers 3 are arranged between the 6 evenly distributed horizontal runners, and the positions of the risers are close to the inner hole of the guide plate cavity 1. In order to ensure the shrinkage compensation effect, this embodiment adopts heat preservation heating risers.

[0069] During smelting, the present embodiment adds Y and Ce elements that meet the content range and 1 kg of silicon-zirconium inoculant per ton of molten steel. Before tapping, the steel is placed in a ladle and then poured into the molten steel. The tapping temperature is 1475°C. After tapping, argon is blown in the ladle for 30 seconds and then calmed to 1380°C for casting. After obtaining the blank, conventional annealing and rough machining are performed, and then quenching and tempering treatment is performed. The quenching and tempering process is as follows: the heating temperature is 940°C, the isothermal temperature is 320°C, and the isothermal time is 85 minutes. The tempering temperature is 420°C, and secondary tempering is performed at 200°C.

[0070] After quenching and tempering, this embodiment is subjected to conventional machining to the finished product, and hardness testing is performed at the minimum outer diameter 6 of the working surface. The hardness test results are HRC values: 42.5, 42.0, 41.8, 42.6, 41.7, 42.3, with an average of 42.15HRC; the conjoined specimens are subjected to tensile performance testing, and the results are σb values ​​of 591MPa, 590MPa, 589MPa, and 590MPa, respectively, with an average of 590MPa. The second piece HRC values: 41.9, 42.1, 41.8, 42.3, 42.6, 42.4, with an average of 42.18HRC; the conjoined specimens are subjected to tensile performance testing, and the results are σb values ​​of 587MPa, 589MPa, 601MPa, and 592MPa, respectively.

[0071] During the installation and production process, this embodiment has the effect of increasing the service life by 4 times compared with the existing ductile iron guide disc. When it is scrapped, the outer diameter of the working surface is reduced by 85mm, and the surface hardness is still around 50HRC, which saves materials and reduces production costs.

[0072] The present invention adopts multi-component composite strengthening materials for the guide disc components of the steel pipe rolling mill, and adopts a new casting system and a reasonable preparation process and heat treatment method, so that the comprehensive properties of the guide disc, such as strength, hardness, toughness and wear resistance, are greatly enhanced, and the "steel sticking" phenomenon that is easily generated by the current alloy ductile iron guide disc during the rolling process is solved, so that the performance and service life of the guide disc of the steel pipe rolling mill are greatly improved, and at the same time, materials are saved and the manufacturing and production costs are reduced.

[0073] The present invention is not limited to the above embodiments. Those skilled in the art may make various improvements or modifications to the present invention without departing from the design concept of the present invention. These changes and modifications should fall within the protection scope of the present invention.

Claims

1. A high chromium guide plate for a steel tube rolling mill, characterized in that: Its composition is calculated by weight as follows: C: 1.5% ~ 1.7%, Si: 0.6% ~ 1.0%, Mn: 0.4% ~ 0.8%, P: ≤ 0.04%, S: ≤ 0.02%, Cr: 12.0% ~ 13.0%, Al: 3.6% ~ 4.0%, Ni: 0.2% ~ 0.3%, Mo: 0.1% ~ 0.2%, Nb: 0.1% ~ 0.2%, Y: 0.02% ~ 0.025%, Ce: 0.09% ~ 0.11%, N: 0.008% ~ 0.01%, and the balance is Fe and other inevitable impurities.

2. The high chromium guide plate according to claim 1, characterized in that: The composition is calculated by weight as follows: C: 1.6%, Si: 0.8%, Mn: 0.6%, P: ≤0.04%, S: ≤0.02%, Cr: 12.5%, Al: 3.8%, Ni: 0.25%, Mo: 0.15%, Nb: 0.15%, Y: 0.02%, Ce: 0.10%, N: 0.009%, and the remainder is Fe and other inevitable impurities.

3. A high chromium guide plate casting system for a steel tube rolling mill according to claim 1, characterized in that: The casting system is provided with a guide plate cavity above and a system platform and a platform bracket below; a molten steel runner and a riser are provided above the guide plate cavity, the molten steel runner is provided with a vertical runner in the middle connecting a number of evenly distributed horizontal runners, and a number of risers are evenly distributed between the horizontal runners; the molten steel runner and the riser are both connected to the guide plate cavity.

4. The casting system according to claim 3, characterized in that: The outer circle and lower part of the guide disc cavity adopt improved sand mold, and the sand mold forming the guide disc cavity 1 is placed in a circular ring-shaped sand box with an inner hole; from the top of the circular ring-shaped sand box to the center position of the inner hole, several horizontal runners of the molten steel runner are evenly distributed on the upper part of the guide disc cavity.

5. The casting system according to claim 4, characterized in that: The system platform is a circular platform with a diameter larger than the outer circle of the annular sand box. The annular sand box is arranged on the system platform supported by the platform bracket.

6. The casting system according to claim 3, characterized in that: The riser is arranged above the guide disc cavity and close to the inner hole.

7. A method for preparing the high chromium guide plate of a steel tube rolling mill according to claim 1 or claim 3, characterized in that: The high chromium guide disc is prepared by using the composition of the high chromium guide disc described in claim 1 and the casting system described in claim 3, and the method is as follows: 1) preparing a circular sand box with an inner hole in the guide plate cavity; adding 60-75% of the total weight of graphite particles to the molding sand to prepare an improved sand mold, and using the improved sand mold in the outer circumference and lower part of the guide plate cavity to increase the ability of these parts to be evenly cooled; 2) Molten steel is smelted according to the composition range of the guide plate, and the tapping temperature is 1460℃~1490℃; before tapping, 1kg of silicon-zirconium inoculant per ton of molten steel and Y and Ce elements that meet the composition content range are put into the ladle and then poured into the molten steel to spheroidize the alloy; 3) After steel is tapped, argon is blown into the ladle for 30 seconds to calm it down to 1370℃~1400℃ for casting; 4) Molten steel is poured through the vertical runner of the casting system and flows evenly to each horizontal runner until the molten steel in the circular sand box of the guide plate cavity fills the casting from bottom to top to obtain a guide plate blank; then the cast guide plate blank is subjected to conventional annealing and rough processing; 5) After rough machining, the guide plate is subjected to salt bath isothermal quenching and tempering heat treatment process; the heating temperature of salt bath isothermal quenching is 920-950°C, the isothermal temperature is 290°C-320°C, and the isothermal time is 60-90min; the tempering temperature is 420°C, and the secondary tempering is 200°C; 6) After the heat treatment is completed, the guide plate is machined into a finished product.

8. The preparation method according to claim 7, characterized in that: Routine steps such as argon blowing in the steelmaking process are carried out in a conventional manner to ensure the quality of the steelmaking process.

9. The preparation method according to claim 7, characterized in that: The preferred composition range of the guide disc components is calculated by weight as follows: C: 1.6%, Si: 0.8%, Mn: 0.6%, P: ≤0.04%, S: ≤0.02%, Cr: 12.5%, Al: 3.8%, Ni: 0.25%, Mo: 0.15%, Nb: 0.15%, Y: 0.02%, Ce: 0.10%, N: 0.009%, and the remainder is Fe and other inevitable impurities.

10. The preparation method according to claim 7 or 9, characterized in that: The tensile strength of the guide disc is 550MPa-650MPa, and the surface hardness is HRC40-55.

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